Electromagnetic valve for controlling an injection valve of an internal combustion engine

ABSTRACT

The present invention is directed to a solenoid valve for controlling a fuel injector in an internal combustion engine, having an electromagnet, an armature having an armature pin which is movably supported with respect to the electromagnet, and an armature plate supported on the armature pin in a manner allowing sliding movement, and a control-valve member moved together with the armature and cooperating with a valve seat to open and close a fuel discharge passage, the armature plate, in response to the control-valve member striking the valve seat during the closing of the solenoid valve, being able to be moved, under the influence of its own inert mass, along the armature pin along an overtravel distance, from a stop secured to the armature pin up to a stationary overtravel stop. To avoid post-oscillations of the armature plate on the armature pin when closing the solenoid valve, the armature plate is supported on the armature pin between the overtravel stop and the stop secured to the armature pin, in a manner that is free of returning elastic spring forces and allows sliding movement.

BACKGROUND INFORMATION

A solenoid valve, which is known, for example, from German PatentApplication No. DE 196 50 865, is used for controlling the fuel pressurein the control pressure chamber of a fuel injector, for example, of aninjector of a common-rail injection system. In such injection valves,the fuel pressure in the control pressure chamber controls the movementof a valve plunger with which an injection orifice of the injectionvalve is opened or closed. The known solenoid valve features anelectromagnet located in a housing part, a movable armature and acontrol-valve member which is moved together with the armature and actedupon in the closing direction by a closing spring. The control-valvemember cooperates with a valve seat of the solenoid valve, therebycontrolling the fuel discharge from the control pressure chamber.

A known disadvantage of the solenoid valves consists in the so-calledarmature bounce. When the magnet is deenergized, the closing spring ofthe solenoid valve accelerates the armature and, with it, thecontrol-valve member toward the valve seat in order to close a fueldischarge passage from the control pressure chamber. The impact of thecontrol valve member on the valve seat causes disadvantageousoscillations and/or bouncing of the control-valve member at the valveseat, which has a detrimental effect on the control of the injectionprocess. For this reason, the solenoid valve known from German PatentApplication No. DE 196 50 865 has an armature that is designed in twoparts and includes an armature pin and an armature plate slidablysupported on the armature pin, so that, when the valve control memberstrikes the valve seat, the armature plate continues its movementagainst the elastic force of a return spring. Subsequently, the returnspring returns the armature plate to its defined original position at astop secured to the armature pin. In this way, the armature plate ispulled up at an always identical, predefined distance when theelectromagnet is reenergized.

While the effectively decelerated mass and, thus, the kinetic energy ofthe armature striking the valve seat, which causes the bouncing, areindeed reduced by the two-piece design of the armature with therestoring spring, the armature plate, upon which the spring force of therestoring spring acts, may oscillate on the armature pin in adisadvantageous manner once the solenoid valve is closed. During thepost-oscillation process, the armature plate may strike the stop securedto the armature pin, thereby briefly opening the solenoid valve. Thisbrief opening does not cause a significant pressure drop in thecontrol-pressure chamber of the fuel injector and, thus, an unintendedinjection. However, the activation of the electromagnet for the nextinjection may not be initiated during this brief phase since this wouldaffect the fuel quantity injected into the combustion chamber of theinternal combustion chamber in an undefined manner, and cause seriousdeviations in the injection quantity. Therefore, a defined injectionquantity will only be achieved again in a reliable manner once thearmature plate has stopped oscillating. Restricting the duration of thepost-oscillation process is of great importance, especially forrepresenting short time intervals between, for instance, a pre-injectionand a main-injection. For this reason, known solenoid valves use a fixedovertravel stop which restricts the maximum overtravel distance by whichthe armature plate may move on the armature pin subsequent to thecontrol-valve member striking the valve seat. However, while thismeasure may reduce the post-oscillations of the armature plate, itcannot stop them.

SUMMARY OF THE INVENTION

It has been discovered that, if the return spring is entirely omitted,it is possible not only to avoid disadvantageous post-oscillations ofthe armature plate in a solenoid valve having a two-part armature, butto implement a defined injection in a new activation of theelectromagnet at the same time as well. Contrary to a long-heldmisconception, the restoring spring is not absolutely necessary toensure a defined new injection. Since the overtravel stop makes itpossible to limit to a small amount the distance by which the armatureplate may move on the armature pin once the control-valve member strikesthe valve seat, a defined new injection may be achieved even in theabsence of a restoring spring. While it is true that the armature plateis not returned to the stop secured to the armature pin when therestoring spring is omitted, the armature plate is attracted so quickly,however, once the electromagnet is energized that it reaches the stop atthe armature pin with practically no noticeable time delay. The armatureplate and the armature pin with the control-valve member, thereupon, areaccelerated toward the electromagnet, and the solenoid valve is opened.In this manner, the undesired opening of the solenoid valve, due to thepost-oscillations of the armature plate, is prevented in an advantageousmanner, so that the solenoid valve is able to be reactivated at any timeonce the armature plate has reached its overtravel stop.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section of the upper part of a fuel injector having asolenoid valve as known from the related art.

FIG. 2 shows the valve travel of the armature plate for the knownsolenoid valve as a function of time.

FIG. 3 shows a cross-sectional representation of the solenoid valveaccording to the present invention.

FIG. 4 shows the valve travel of the armature plate for the solenoidvalve according to the present invention as a function of time.

DETAILED DESCRIPTION

FIG. 1 shows the upper part of a fuel injector known from the relatedart, which is intended to be used in a fuel injection system,particularly in a common rail system for diesel fuel equipped with afuel high-pressure reservoir that is continually supplied withhigh-pressure fuel by a high-pressure fuel booster pump. The known fuelinjector includes a valve housing 4 having a longitudinal bore, in whicha valve plunger 6 is positioned, whose one end (not shown in Figure)acts upon a valve needle positioned in a nozzle body. The valve needleis disposed in a pressure chamber, which is supplied with fuel underhigh pressure via a pressure bore. During an opening stroke of valveplunger 6, the valve needle is lifted up, against the closing force of aspring, by the high fuel pressure in the pressure chamber, whichcontinuously acts on a pressure shoulder (an exposed annular area) ofthe valve needle. Via an injection orifice, which is then connected tothe pressure chamber, the fuel is injected into the combustion chamberof the internal combustion engine. By lowering valve plunger 6, thevalve needle is pressed into the valve seat of the fuel injector in theclosing direction, completing the injection process. Valve plunger 6, byits end facing away from the valve needle, is guided in a cylindricalbore, which has been introduced in a valve piece 12 set into valvehousing 4. In the cylindrical bore, the end face of valve plunger 6encloses a control-pressure chamber 14, which is connected to a fuelhigh-pressure connection (not shown) via a supply channel.

The inlet passage is essentially designed in three parts. A bore, whoseinner walls form a supply throttle 15 along part of their length,extends radially through the wall of valve piece 12 and is constantlyconnected to an annular space 16 that surrounds valve piece 12 on itsouter circumference, which annular space, in turn, is in constantconnection to the fuel high-pressure connection. Via inlet throttle 15,control pressure chamber 14 is subjected to the high fuel pressurepresent in the high-pressure fuel accumulator. Coaxially to valveplunger 6, a bore branches off from control pressure chamber 14, thebore running in valve piece 12 and forming a fuel discharge passage 17which is provided with a discharge throttle 18 and empties into a reliefchamber 19 which is connected to a low-pressure fuel connection 1 (notshown in FIG. 1) which, in turn, is connected to the fuel return of fuelinjector 1. The outlet of fuel discharge passage 17 from valve piece 12occurs in the region of a conically countersunk piece 21 of the externalend face of valve piece 12. Valve piece 12, together with an adjustmentdisk 38 and flange 32 of a sliding block 34, is fixedly braced in valvehousing 4 via a screw member 23.

A valve seat 24, with which a control-valve member 25 of a solenoidvalve 30 controlling the fuel injector cooperates, is formed in conicalpart 21. Control-valve member 25 is coupled to a two-part armature inthe form of an armature pin 27 and an armature plate 28, the armaturecooperating with an electromagnet 29 of the solenoid valve 30. Solenoidvalve 30 also includes a housing part 60 accommodating electromagnet 29,which is firmly connected to valve housing 4 via connecting means 7which may be screwed together. In the known solenoid valve, armatureplate 28 rests on armature pin 27, in such a manner that it isdynamically movable against the prestressing force of a return spring 35under the action of its inertial mass and, in the resting state, ispressed via this return spring against a stop 26, which is secured tothe armature pin and designed as a crescent disk slipped over thearmature pin. By its other end, return spring 35 is supported at flange32 of sliding block 34, which guides armature pin 27 in a feed-throughopening. Armature pin 27 and, with it, armature plate 28 and controlvalve member 25 which is coupled to armature pin 27, are permanentlyacted upon in the closing direction by a closing spring 31 which isimmovably supported relative to the housing, so that control valvemember 25 normally rests against valve seat 24 in the closed position.When the electromagnet is energized, armature plate 28, and with itarmature pin 27, is attracted by the electromagnet and, in the process,discharge passage 17 is opened toward relief chamber 19. Armature pin27, at the end facing away from electromagnet 29, has an annularshoulder 33, which strikes sliding block 34 when the electromagnet isenergized and, in this manner, limits the opening lift of control-valvemember 25. Adjustment disk 38 may be used to adjust the opening lift.

The opening and closing of the fuel injector are controlled by solenoidvalve 30 as described below. As explained previously, armature pin 27 isconstantly acted upon in the closing direction by closing spring 31, sothat control-valve member 25 lies against valve seat 24 in the closingposition when the electromagnet is not activated, and control pressurechamber 14 is closed towards pressure relief side 19. As a result, thehigh pressure present in the fuel high-pressure reservoir very rapidlybuilds up there as well, via the supply channel. The pressure in controlpressure chamber 14 generates a closing force on valve plunger 6, andthus on the valve needle connected with it, which is greater than theforces acting on the other side in the opening direction as a result ofthe high pressure present. When control pressure chamber 14 is openedtoward relief side 19 by the opening of the solenoid valve, the pressurein the small volume of control pressure chamber 14 is reduced veryquickly, since the control pressure chamber is decoupled from the highpressure side via inlet throttle 15. As a consequence, the force of thehigh fuel pressure present at the valve needle, which acts on the valveneedle in the opening direction, predominates, so that the valve needleis moved upward and, in the process, the at least one injection orificeis opened for injection. However, when solenoid valve 30 closes fueldischarge passage 17, the pressure in control pressure chamber 14 isable to be built up again by the subsequent flow of fuel via supplychannel 15, so that the original closing force is present, closing thevalve needle of the fuel injector.

When the solenoid valve is closed, closing spring 31 rapidly pressesarmature pin 27 with control-valve member 25 against valve seat 24. Adisadvantageous bounce or post-oscillating of the control-valve memberis the result of the elastic deformation of the valve seat caused by theimpact of the armature pin on the valve seat, which acts as an energystore. Part of the energy, in turn, is transmitted to control-valvemember 25, which then bounces off from valve seat 24 together with thearmature pin. The known solenoid valve shown in FIG. 1, therefore, usesa two-part armature with an armature plate 28 that is decoupled fromarmature pin 27. In this manner, the overall mass striking valve seat 24may be reduced, but armature plate 28 may have disadvantageouspost-oscillations. For this reason, the known solenoid valve is providedwith an overtravel stop 37, which is formed by an end piece facing thearmature plate of a section of sliding member 34 designed as a guidesleeve. Overtravel stop 37 limits the maximal overtravel distance bywhich armature plate 28 may move along armature pin 27 from stop 26,secured to armature pin 27, after control-valve member 25 has struckvalve seat 24. Overtravel stop 37 reduces the post-oscillations ofarmature plate 28, and armature plate 28 returns more quickly to itsoriginal position at stop 26 in the form of a crescent disk.

In FIG. 2, the lift curve of the armature plate is shown as a functionof time during the opening of the solenoid valve. When the solenoidvalve is closed, armature plate 28, in a first time interval I,initially moves with armature pin 27 by distance h1 of, for instance, 38micrometer, until the control-valve member strikes the valve seat ath=0. Subsequently, armature plate 28, in time interval I, moves furtherby the overtravel distance until striking overtravel stop 37, travelinga maximum overtravel distance h2 of, for instance, approximately 20micrometer, and is stopped there. In the then following time intervalII, return spring 35 moves the armature plate back, up to crescent disk26. In time interval III, the armature plate lifts off the armature pinand the control-valve member from the valve seat, thereby causingsolenoid valve to open briefly. When the armature plate swings back, thecontrol-valve member again strikes the valve seat at the beginning oftime interval IV. Due to the oscillations of the armature plate, norenewed activation of the solenoid valve is able to be initiated in timeinterval III, since the solenoid valve briefly opens in this timeinterval. Therefore, the activation of the solenoid by applying voltageto the electromagnet must only occur either before, in time interval II,or after, in time interval IV.

FIG. 3 shows a cut-out of a cross-sectional representation of thesolenoid valve, designed according to the present invention. Solenoidvalve 30 according to the present invention differs from the knownsolenoid valve represented in FIG. 1 in that no return spring isprovided at the solenoid valve. When electromagnet 29 is switched off,closing spring 31 moves the armature with armature plate 28, armaturepin 27 and control-valve member 25 toward valve-seat 24. As soon as thecontrol-valve member strikes valve-seat 24, armature plate 28, due toits inert mass, continues its movement on the now stationary armaturepin. This movement of armature plate 28 is only subject to the laws ofinertia, gravity, friction and the hydrodynamics of the fuel, and occurswithout stress from a returning elastic spring force. The resultingmovement of armature plate 28 is shown in FIG. 4. As illustrated in theknown solenoid valve in FIG. 2, armature plate 28, in time interval I,initially moves with the armature pin by the opening valve travel h1,and subsequently, after the control-valve member has struck the valveseat, given a stationary armature pin, by the overtravel lift h2 up toovertravel stop 37, where armature plate 28 remains. The circularsurface 39, adjacent to overtravel stop 37, of a nipple 40, which isformed at armature plate 28 and slipped over armature pin 27, forms ahydraulic damping chamber together with overtravel stop 37, by which theimpact of armature plate 28 on the overtravel stop is damped. As can beseen in FIG. 4, no post-oscillations of the armature plate and nofurther opening of the solenoid valve occur in time interval II when theelectromagnet is switched off. Therefore, the solenoid valve accordingto the present invention may be reactivated at any time as soon as thearmature plate has reached its position at the overtravel stop.

If voltage is applied to the electromagnet during the opening of thesolenoid valve, armature plate 28, due to the then acting magneticforce, is advanced very rapidly, by distance h2, up to stop 26 securedto the armature pin. The time delay, until the armature plate reachesstop 26, may be negligible in this case. This assumes that the maximumovertravel lift h2 is not too great. Therefore, the maximum overtraveldistance by which armature plate 28 may move along armature 27 from stop26 secured to the armature pin, after control-valve member 25 has struckvalve seat 24 during the closing of the solenoid valve, should be lessthan 100 micrometer, and preferably less than 30 micrometer.

1. A solenoid valve for controlling a fuel injector of an internalcombustion engine, comprising: an electromagnet; an armature includingan armature pin that is movably supported with respect to theelectromagnet; a control-valve member moving with the armature andcooperating with a valve seat, to open and close a fuel passage; and anarmature plate supported on the armature pin in a manner that allowssliding movement, the armature plate capable of being moved along thearmature pin when the control-valve member strikes the valve seat duringa closing of the solenoid valve, under the influence of its own inertmass, from a stop secured to the armature pin right up to a stationaryovertravel stop about an overtravel path, the armature plate beingsupported on the armature pin between the overtravel stop and the stopsecured to the armature pin, in a manner that is free of returningelastic spring forces and that allows sliding movement.
 2. The solenoidvalve according to claim 1, wherein a maximum overtravel distance, aboutwhich the armature plate may shift along the armature pin after thecontrol-valve member strikes the valve seat during the closing of thesolenoid valve, starting from the stop secured to the armature pin rightup to the striking of the overtravel stop, is less than 100 micrometers.3. The solenoid valve according to claim 2, wherein the maximumovertravel distance is less than 30 micrometers.